Knowing What Makes Windows Energy Efficient Can Save You Money

March 26, 2018

When it comes to increasing energy efficiency in your home, it’s easy to ignore the impact your windows have on your energy costs. Drafty windows are easy to identify, but you don’t need to have a noticeable issue with your windows to benefit from replacement windows. The right windows can help you save costs when it comes to heating and cooling your home.

Thanks to modern technologies, the glass in your windows can increase energy efficiency. And that doesn’t just mean tinting your windows. Multiple-pane choices, various types of glazing, gas fills, and even the method used to install the glass can help you save money on your energy bills throughout the year, regardless of the weather.

Get to Know the ENERGY STAR® Basics
When selecting windows for energy efficiency, it's important to first consider their energy-performance ratings in relation to the Portsmouth climate and your home's design. What does “energy efficiency” even mean and how can you weigh the energy savings of one window against another once they’re installed?

ENERGY STAR is a government-backed symbol that provides consumers with a dependable source for energy efficiency information about products. When buying an energy-efficient window, look for the ENERGY STAR label. It will list a number of the factors that go into identifying performance. Here’s a look at what these categories mean:

U-Factor: The rate of heat loss to the outside. A low U-factor is better.

Solar Heat Gain Coefficient (SHGC): Normally listed as a fraction, this is the amount of solar radiation that a window lets in. SHGC is measured on a scale from 0 to 1. Window SHGC usually ranges from 0.25 to 0.80. Again, a low number is better.

Air Leakage (AL): The rate at which air passes through the joints in the window. The lower the AL value, the less air leakage.

Visible Transmittance (VT): The amount of light the window lets through measured on a scale of 0 to 1, with values generally ranging from 0.20 to 0.80. The higher the VT, the more light you see.

Condensation Resistance Factor (CRF): How consistently the window resists water buildup on a scale from 0 to 100. The higher the CRF, the better the window will withstand condensation.

Make sure to look for scores based on whole-unit numbers as opposed to center-of-glass numbers (COG). Whole-unit numbers are more reliable indicators of the window’s overall performance, while COG numbers may not be as consistently reliable in areas of the window farther away from the center.

More Panes, Less Pain
Energy efficiency is improved in windows with more panes of glass in them. Double-pane windows are a notable choice for homeowners looking to improve energy efficiency with replacement windows.

While they can cost more, triple-pane windows can offer even higher energy efficiency that is worth the expense. Adding a middle pane means greater protection against the elements and allows the inner pane of the window to stay truer to room temperature. A third pane also cuts down any convection currents and drafts that could make a room chillier.

Beyond improving energy efficiency, triple-pane windows also bring greater protection against loud noises and break-in damage than double-pane replacement windows. So, if you have loud neighbors or live on a heavy-traffic street, you might benefit from triple-pane windows.

More Than Just Tinting
The glazing on your window can play a large role in reducing both the SHGC and VT that factors into ENERGY STAR ratings. For years, people have used tinted glazing to absorb sunlight and reduce glare. Two other options can help on both sides of the glass and increase energy efficiency in your home.

On windows with two or more panes of glass, insulated glazing is created when the glass panes are spaced apart and hermetically sealed, leaving an insulating air space. Insulated window glazing mostly lowers the U-factor, but it also lowers the SHGC.

Low-e coating can also have an impact on energy efficiency. A microscopically thin, virtually invisible metal or metallic oxide layer placed directly on the surface of one or more of the panes of glass, low-e coating helps decrease the window’s U-factor and can reduce energy loss by as much as 30 to 50 percent.

Insulating with Gas
Increasingly common in modern homes, gas-filled windows are made of at least two panes of glass with either argon or krypton gas filling the space between each one. This gas makes another invisible barrier against the heat and cold that would effect a window’s U-factor or leakage rate.

Argon and krypton are nontoxic, naturally occurring gasses found in the air we breathe. Factory sealing the gas between the window’s glazing layers reduces the possibility of leakage or condensation buildup on the interior and exterior of your windows.

Edge Spacers Seal Out Leaks
The final factor that helps improve a window’s energy efficiency is the edge spacer. Edge spacers serve a range of functions. They:

bear the stress the window faces with expansion and contraction during times of heat and cold.

provide a moisture barrier to resist water or vapor condensation.

provide a gas-tight seal that prevents the loss of any gas in low-e windows.

Windows are available in single-seal or double-seal systems. Aluminum seals are most common due to the material’s strong energy-conducting traits.

Single-seal systems use an organic sealant applied behind the spacers that holds the unit together and resists moisture leakage. A double-seal system includes a secondary backing sealant, often silicon, to further defend against leaks. Double-seal systems are most often seen in low-e windows to prevent any of the sealed gasses from escaping.

There’s a lot of science that goes into making an energy-efficient replacement window. But, by reviewing the basics of what goes into the ENERGY STAR rating and understanding the differences in window glass options, you can discover windows that will make your home temperate and save you money at the same time.

Learn more about energy efficiency in your windows by visiting our professionals at Pella of Portsmouth. Call 603-427-0677 or stop by our showroom. You can also schedule an appointment online for a free, in-home consultation.